I am trying to change which dictionary is used in the Reader. I went into the preferences, added the URL for a dictionary with {word} in the right place. But the reader doesn't pick up my change and defaults to installed dictionary mode. I don't see any "okay" or anything to click after I add the URL. What am is missing to make the dictionary I want be the default?

By 'reader', you mean the Calibre Viewer?
For that, you go to preferences (INSIDE the viewer): Dictionaries (tab) use
ADD website (button) : set the language: Set the URL and remember to end that with /{word}

I am trying to change which dictionary is used in the Reader. I went into the preferences, added the URL for a dictionary with {word} in the right place. But the reader doesn't pick up my change and defaults to installed dictionary mode. I don't see any "okay" or anything to click after I add the URL. What am is missing to make the dictionary I want be the default?

Moderator Notice

@MarcoDiWA - I moved your post because the 'dictionaries' used by the Editor and Reader are different beasts. The first is a sophisticated wordlist used for spell checking - known as hunspell files. The second is a link to an online dictionary.